The present invention relates to the field of computer disk drives, and more particularly, the invention relates to a latch mechanism for latching a read/write head actuator of a disk drive wherein at least one contacting surface of the latch mechanism includes a soft metallic coating or plating to reduce friction and particle generation.
In a typical computer disk drive, an area of each disk serves as a landing area for the read/write heads. The disk drive employs a latching mechanism to hold the read/write heads over the landing area during spin-up, spin-down, and power down of the disk drive. The landing area is a portion of the disk not used for data storage. Typically, the landing area is located on the disk tracks closest to the center of the disk. The failure to latch the read/write heads during spin-up, spin-down, or power down of the disk drive results in the read/write heads bouncing on or otherwise improperly contacting data areas on the disk which results in corruption of stored data, and damage to the disk.
A number of prior art latching mechanisms exist. One type or category of latching mechanism is one which requires physical contact of a portion of the actuator assembly against a latch stop. Another type of latching mechanism is one which utilizes magnetic flux for capturing and holding a latch tab of the actuator assembly without contacting a latch stop. While some non-contact latching mechanism may be adequate for their intended purposes, one problem associated with such mechanisms is that they suffer from wide variations in latching force due to manufacturing tolerances which do not allow repeatability in terms of creating a latching force of consistent magnitude. For contact type latching mechanisms, while some of these may be adequate for their intended purposes, many of these devices suffer from being structurally complex and difficult to manufacture, thus adding unnecessary complexity and cost to the disk drive as a whole.
One example of a passive non-contact magnetic latch is disclosed in the U.S. Pat. No. 5,742,453. This reference discloses a magnetic latch which has a magnetic circuit for capturing a latch tab of an actuator assembly. Magnetic flux lines traverse the latch tab in a direction substantially perpendicular to a direction of movement of the latch tab.
An example of a contact latch mechanism is disclosed in U.S. Pat. No. 5,812,345. The latch mechanism of this invention utilizes a permanent magnet to bias an elongated rotatable latch arm into engagement with the actuator when the actuator is positioned in the landing zone. An electromagnetic coil, positioned between the magnet and the magnetic return plates, when energized, counters this bias permitting the latch arm to rotate out of engagement with the actuator. Other examples of latching mechanisms include those disclosed in U.S. Pat. Nos. 5,363,261; 5,381,290; 5,377,065; and 5,379,171.
For contact or active latching mechanisms, repeated cycles of contact between contacting elements can cause surface cracking and material failure resulting in particle generation which can contaminate the disk drive. Some disk drives may include contacting surfaces plated with chromium or other high strength, low modulus metals. Over time, such chromium platings are particularly susceptible to developing microcracks causing particle generation. Attempts have been made to apply a liquid lubricant to contacting surfaces of a latch mechanism, such lubricants including Zdol(trademark) and Fombilin(trademark). However, use of any liquid lubricant to reduce friction may actually result in increased contamination. Therefore, use of liquid lubricants has its disadvantages. Consequently, there is a need for an active or contact latch design which reduces particle generation, yet still provides inherent lubrication.
In accordance with this invention, a latch mechanism is provided wherein at least one contacting surface is plated or coated with a soft metal. The soft metal is able to yield and flow under the very high contact loads experienced during disk drive operation, thus preventing particle generation yet providing lubrication at the contact points. In addition to silver, other soft metals may be used to include tin, lead, copper, indium, gold, palladium, platinum, and several of their alloys. In the type of specific latching mechanism disclosed herein, it is preferable to apply the soft metal coating to the latch plate.
The preferred method of applying the coating to the latch plate is electroplating. However, other methods of applying the soft metal coating are contemplated which include sputtering, metal evaporation and cladding.
Preferably, the coating should be thick enough to yield and flow under contact so that the loads transmitted through the coating to the underlying latch do not exceed the plastic stress limits of the latch. Typically, the latch plate is made from stainless steel. In order to accommodate the subsurface plastic contact stress region of a stainless steel latch plate, the thickness of the coating should preferably be in the range from 1 to 20 microns. However, it shall be understood that a coating of a lesser or greater thickness can be used advantageously, and this preferred range of thickness should not be interpreted as a critical range thickness.
The figures discussed below disclose one particular type of disk drive latching mechanism; however, it shall be understood that the coating used on the latch plate disclosed herein can be used with any type of active or contact latch mechanism to reduce particle generation and to provide lubrication.
By the application of a soft metal coating or plating over contact surfaces of a latching mechanism, lubrication can be provided, and particle generation can be minimized without having to redesign the latch mechanism or to make other design changes in the disk drive.